The present invention relates to narrow-profile, terminal block relays and in particular to a method of adding electrical fuses or other components to such relays.
“European style” terminal blocks provide a method of electrical interconnection of industrial control components. These terminal blocks have a narrow and flat shape that allows them to be stacked together in close proximity when mounted on a DIN rail. When so stacked, wires may be received at terminals along the upper and lower edge of the terminal blocks.
The terminals allow connection to other wires connected to other terminals or to the leads of electrical components supported by the terminal block. Such electrical components may include fuses, indicator lights, and relays.
For a terminal block holding a relay (“a terminal block relay”) or a fuse (“a terminal block fuse”), the relay or fuse is typically received by a socket at the front edge of the terminal block. The housings holding the relay or fuse are designed to have a width no greater than that of the terminal block, typically between 5 to 14 mm, to minimize space occupied on the DIN rail.
Programmable logic controllers (PLCs) are industrial computers used for the control of machines and processes. A PLC has input and output circuits that may connect to sensors and actuators on controlled machines and by executing a standard control language, such as relay ladder language, the PLC may read the inputs and according to the execution of the control program and provide outputs controlling the machine.
Terminal block relays are often used with a PLC, the latter which may be attached to the same DIN mounting rail on which the terminal block relays are mounted. Outputs from the PLC are connected to the coils of terminal block relays whose contacts in turn connect to the desired machine actuator to provide a form of isolation.
When the contacts of a terminal block relay are connected, for example to an inductive load, a fuse may be placed in series with those contacts. This normally entails placing a fuse terminal block adjacent to each terminal block relay doubling the required space needed on the mounting rail. When many outputs to inductive loads are required, the amount of space on the rail is quickly exhausted. A similar problem arises when other components are added to the terminal block relay, including timing circuits or voltage suppressors.